An inverter is a power conversion circuit including a switching element. Pulse width modulation (PWM) control is one of representative methods applied to control inverters. When the PWM control method is applied to control an inverter, a carrier wave and a signal wave are compared to generate a gate signal for controlling a switching element.
Generally, a three phase PWM inverter generates common mode voltage. The common mode voltage includes a zero phase harmonic component.
Japanese Patent Laying-Open No. 2008-271617 (PTD 1) discloses a power conversion device that allows a motor to have a low speed range with a waveform characteristic held equivalent to a conventional, three phase modulation system and also reduces electromagnetic wave. The power conversion device generates three triangular wave carriers corresponding to three phases, respectively, independently from each other. Furthermore, the three triangular wave carriers are provided with a phase difference. For example, one of the triangular wave carriers is increased in frequency to be temporarily higher in frequency than the others of the triangular wave carriers.
Japanese Patent Laying-Open No. 2005-051959 (PTD 2) discloses a configuration for reducing a leakage current of a power conversion device. This configuration allows a voltage command value for each phase and a triangular wave to be compared to generate three pulsing signals. When two pulsing signals are simultaneously generated, one pulsing signal is delayed relative to the other pulsing signal.